module Main where

import Data.List
import Data.Maybe
import Data.Word
import Data.Tuple
import Control.Arrow
import Control.Monad
import qualified Crypto.Hash.SHA256 as SHA256
import qualified Data.ByteString as B

fromBase :: Integral a => Integer -> [a] -> Integer
fromBase b = foldl (\a c -> fromIntegral c + a * b) 0

toBase :: Num a => Integer -> Integer -> [a]
toBase b = reverse . unfoldr f where
 f 0 = Nothing
 f n = Just $ first fromInteger $ swap $ n `divMod` b


b58chars = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"

b58encode :: [Word8] -> [Char]
b58encode l = replicate (length $ takeWhile(==0) l) '1' ++ 
	  (map (b58chars!!) . toBase 58 . fromBase 256) l

fromb58char c = fst . fromJust . find ((==c) . snd) $ zip [0..] b58chars

b58decode v = 
  case span (== b58chars !! 0) v of
    (ones, v) -> 
      replicate (length ones) 0 ++
        (toBase 256 . fromBase 58 . map fromb58char) v

b58decodeL l v = 
  let 
    res = b58decode v 
  in
    guard (length res == l) >> return res

sha256x2 = B.unpack . SHA256.hash . SHA256.hash . B.pack where

checksum = take 4 . sha256x2

mkAddress :: Word8 -> [Word8] -> [Char]
mkAddress v d = b58encode $ v : d ++ checksum (v : d)

validateAddress :: [Char] -> Maybe (Word8, [Word8])
validateAddress addr = do
  (version : d) <- b58decodeL 25 addr
  case splitAt 20 d of
    (d, check) -> do
      guard $ checksum (version : d) == check
      return (version, d)